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Postlesional epilepsy: the ultimate brain plasticity
K M Jacobs1, K D Graber, V N Kharazia
1Department of Neurology and Neurological Sciences, Stanford University Medical Center, California 94305, USA. kmjake@leland.stanford.edu
Abstract:
Lesions that occur either during fetal development or after postnatal brain trauma often result in seizures that are difficult to treat. We used two animal models to examine epileptogenic mechanisms associated with lesions that occur either during cortical development or in young adults. Results from these experiments suggest that there are three general ways that injury may induce hyperexcitability. Direct injury to cortical pyramidal neurons causes changes in membrane ion channels that make these cells more responsive to excitatory inputs, including increases in input resistance and a reduction in calcium-activated potassium conductances that regulate the rate of action potential discharge. The connectivity of cortical circuits is also altered after injury, as shown by axonal sprouting within pyramidal cell intracortical arbors. Enhanced excitatory connections may increase recurrent excitatory loops within the epileptogenic zone. Hyperinnervation attributable to reorganization of thalamocortical, callosal, and intracortical circuitry, and failure to prune immature connections, may be prominent when lesions affect the developing neocortex. Finally, focal injury can produce widespread changes in gamma-aminobutyric acid and glutamate receptors, particularly in the developing brain. All of these factors may contribute to epileptogenesis.
Insights
Brain lesions from injury or developmental issues can cause hard-to-treat seizures. Research reveals three key mechanisms: neuronal excitability changes, altered brain circuit connectivity, and receptor modifications, all contributing to epileptogenesis.
Area of Science:
- Neuroscience
- Epileptology
- Developmental Neuroscience
Background:
- Brain lesions, whether from fetal development or postnatal trauma, frequently lead to intractable seizures.
- Understanding the underlying epileptogenic mechanisms is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the epileptogenic mechanisms associated with cortical lesions in animal models.
- To identify how injuries during development versus adulthood influence seizure generation.
Main Methods:
- Utilized two distinct animal models to simulate cortical lesions.
- Examined changes in neuronal excitability, circuit connectivity, and receptor function post-injury.
Main Results:
- Cortical injury alters neuronal ion channels, increasing excitability (e.g., increased input resistance, reduced potassium conductance).
- Axonal sprouting and reorganization of neural circuits (thalamocortical, callosal, intracortical) enhance excitatory connections.
- Lesions, especially in the developing brain, cause widespread changes in inhibitory (GABA) and excitatory (glutamate) receptors.
Conclusions:
- Brain injury induces hyperexcitability through direct neuronal effects, altered circuit connectivity, and receptor dysregulation.
- These mechanisms collectively contribute to the development of epilepsy (epileptogenesis).
- The findings highlight distinct and overlapping pathways for seizure generation depending on injury timing (developmental vs. adult).